docs: def db_for_write(self, model, **hints):
          """
          If given some hints['instance'] that is saved in a db, use related
          fields from the same db. Otherwise if passed a class or instance to
          model, return the salesforce alias if it's a subclass of SalesforceModel.
          """
          if 'instance' in hints:
              db = hints['instance']._state.db
              if db:
                  return db
          if getattr(model, '_salesforce_object', False):
              return self.sf_alias